Oriented Film Produced In-Process For Use in the Stretch Film Market

ABSTRACT

Pre-stretched films may be used to increase the rate at which loads can be wrapped and to minimize the exertion required when using conventional stretch films. However, pre-stretched films must generally be stretched in a separate step and stored for several days in order for cling to fully develop. The present disclosure describes compositions, devices, systems, and methods for producing film that eliminate the stretching and storage steps. In particular, the present disclosure relates to the use of selected resins and an angled die to increase the level of orientation in the film as it is formed, thus eliminating the need to stretch the film in a separate step. The present disclosure also relates to the use of a cling agent which eliminates the storage time traditionally required to develop the film&#39;s cling properties.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to compositions, devices,systems, and methods for producing oriented film in-process for use inthe stretch film market. In particular, the present disclosure relatesto the use of selected resins and an angled die to increase the level oforientation in the film as it is formed, thus eliminating the need tostretch the film in a separate step. The present disclosure also relatesto the use of a cling agent which eliminates the storage timetraditionally required to develop the film's cling properties.

BACKGROUND OF THE DISCLOSURE

Stretch films are widely used in a variety of bundling and packagingapplications. For example, manually applied stretch films (i.e.,handheld stretch films) have become a common method of securing bulkyloads such as boxes, merchandise, produce, equipment, parts, and othersimilar items on pallets. Stretch films may be stretched at the time ofuse, which requires the application of force in order to stretch thefilm as much as 200 percent to properly contain the load. In contrast,stretch films may be “pre-stretched” by a film converter prior todelivery to the end-user. Pre-stretched films are described as filmsthat are taken from master rolls of film that have already beenproduced, stretched in a separate step, and re-wound onto film rolls forlater use. Many end-users have chosen to use pre-stretched films toincrease the rate at which loads can be wrapped and to minimize theforce required to wrap loads.

Pre-stretched films are typically made from various polyethylene resinsand may be single or multilayer products. An additive known as a clingagent is frequently used to ensure that adjacent layers of film willcling to each other. A cling agent typically used in pre-stretched filmsis polybutene with a Saybolt Universal Viscosity of 3,000 SUS at99.degree. C. with a number average molecular weight of 1,290. Thiscling agent requires time to migrate or “bloom” to the film's surfaceafter the film is produced and typically starts to reach equilibrium in12 to 24 hours under optimum storage conditions. If the film isstretched before the cling agent has fully migrated, the resulting filmwill have little or no appreciable cling. Films that are produced withexcessive winding tension or stored at low temperatures will also havelittle or no cling due to the lack of migration of the cling agent.

As a result, conventional pre-stretched films require that master rollsof film be stored for several days before stretching in order for thecling agent to migrate and the cling to fully develop. This necessarydelay between the time the film is produced and the time the film isstretched increases the cost and decreases the efficiency of makingpre-stretched films.

After the cling has fully developed, pre-stretched films are stretchedin a separate operation. This process orients the molecules in the filmin a longitudinal direction, parallel to the direction of the film'stravel through the stretching machine. This orientation in the machinedirection removes most of the stretch in the film. The resulting film isrelatively stiff for its thickness and has very little residualorientation or stretch remaining before the film fails in the machinedirection. These characteristics are desirable because much less effortis required to secure a load using pre-stretched film as compared toconventional handheld stretch films. However, this separate operationrequires additional material handling, dedicated converting equipment,increased warehouse space, and the manpower needed to manage theoperation. This process also results in increased film scrap and higherraw material usage, further increasing the cost and decreasing theefficiency of making pre-stretched film.

As can be seen, there is a need for compositions, methods, systems, anddevices which can produce oriented film in a single, continuous process.In addition, there is a need for compositions, methods, systems, anddevices which can simplify the production process by eliminating theneed to stretch the film. Eliminating the stretching and storage stepsmakes oriented film simpler, quicker, and less expensive to produce. Inaddition, the production line may be configured so that the film, asinitially produced, meets the length and width specifications for thefinal product.

SUMMARY OF THE DISCLOSURE

The present disclosure provides an oriented film that is producedin-process and mimics the properties of pre-stretched handheld film. Theoriented film may be comprised of a linear low density polyethylene(LLDPE) copolymer resin. The LLDPE copolymer resin may be blended withresins chosen from the group consisting of polyethylene, polyethylenecopolymers, and polypropylene copolymers. The oriented film may have amajority layer and a plurality of minority layers. The majority layermay be comprised of a LLDPE copolymer resin and the minority layers maybe resins chosen from the group consisting of polyethylene, polyethylenecopolymers, and polypropylene copolymers.

The present disclosure further provides an oriented film that isproduced in-process and contains a cling agent comprised of a polybutenepolymer. The selected cling agent may be a polybutene polymer with aSaybolt Universal Viscosity of 14,900 SUS at 99.degree. C. with a numberaverage molecular weight of 2,060.

The present disclosure further provides an oriented film that isproduced in-process and contains a non-migratory cling agent. Thenon-migratory cling agent may be incorporated into one or more layers ofthe oriented film.

The present disclosure further provides an apparatus for producingoriented film. The apparatus comprises one or more extruders thatreceive and melt the resins. The apparatus also comprises an angled diethat delivers a layer of melted resin from the extruder onto a castingroll to produce a film.

These and other features, aspects, and advantages of the presentdisclosure will become better understood with reference to the followingdrawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood from the following descriptionand the accompanying drawings given as non-limiting examples, and inwhich:

FIG. 1 illustrates the steps for producing oriented cast filmin-process, according to an embodiment disclosed herein;

FIG. 2 illustrates the means for producing a film from molten resins,according to an embodiment disclosed herein;

FIG. 3 illustrates the standard placement of a cast film die accordingto the prior art; and

FIG. 4 illustrates the placement of a cast film die at an angle,according to an embodiment disclosed herein.

DETAILED DESCRIPTION

The following detailed description is of the best currently contemplatedmodes of carrying out the disclosure. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the disclosure, since the scope of the presentdisclosure is best defined by the appended claims.

Broadly, the current disclosure includes compositions, systems, devices,and methods for producing oriented film in-process for use in thestretch film market. More specifically, according to one aspect of thedisclosure, the film may be comprised of higher molecular weight resinsthan are conventionally used for stretch films. The inventive resins mayincrease the level of orientation in the film as it is formed. Inaddition, the resins may be extruded onto the casting roll through anangled die, which may further increase the level of orientation in thefilm. As a result of the increased level of orientation, the film doesnot have to be stretched in a separate operation. Eliminating thestretching step may make the film simpler, quicker, and less expensiveto produce.

In another aspect of the disclosure, a cling agent may be provided toenable an oriented film to be produced without an extensive storage timebetween steps in the manufacturing process. The inventive cling agentdoes not require an extended period of time to migrate to the surface ofthe film. As a result, the cling properties of the film will beimmediately apparent. Eliminating the storage time may further reducethe time and cost associated with producing stretch film.

The film of the present disclosure may be comprised of one layer ormultiple layers, and the composition of each layer may vary. Materialsthat may be used to produce the film layers include, but are not limitedto, Ziegler Natta (ZN) catalyzed linear low density polyethylene(LLDPE), metallocene catalyzed linear low density polyethylene (mLLDPE),polyethylenes, polyethylene copolymers, polyethylene terpolymers,polyethylene blends, polypropylenes, polypropylene copolymers, andblends thereof The majority of the ZN catalyzed LLDPE and mLLDPEmolecules inherently lack long chain branching. In addition, ZNcatalyzed LLDPE has a composition depth breadth index (CDBI), which isdefined as the weight percent of the copolymer molecules having acomonomer content within 50 percent of the medium total molar comonomercontent, of less than 70 percent. As one example, the CDBI of ZNcatalyzed LLDPE may range from 30 to 60 percent. Cling agents may beused as discrete layers or as blends to produce one-sided, differential,or two-sided cling structures. Such cling agents may be migratory ornon-migratory.

One embodiment of the present disclosure may be a three-layer film witha majority layer sandwiched between two minority layers. The thicknessof the minority layers may range from 0 to 49 percent of the total filmthickness. The preferred thickness for the minority layers may beapproximately 16 percent of the total film thickness.

The majority layer may consist of a LLPDE copolymer resin, such as ahigher alpha-olefin LLDPE resin. The melt index of the LLDPE copolymerresin selected for the majority layer may range from 0.5 g/10 min. @190° C./2.16 kg to 4 g/10 min. @ 190° C./2.16 kg, with a preferred meltindex ranging from 0.8 g/10 min. @ 190° C./2.16 kg to 1.2 g/10 min. @190° C./2.16 kg. The density of the LLDPE copolymer resin selected forthe majority layer may range from 0.900 g/cm³ to 0.960 g/cm³, with apreferred density of approximately 0.920 g/cm³. Using a LLDPE copolymerresin with a higher molecular weight than is conventionally used instretch films may increase the level of orientation when the film isextruded through a die. The LLPDE copolymer resin may be also combinedwith other resins, including, but not limited to, other polyethylenes,polyethylene copolymers, and polypropylene copolymers.

The minority layers may be resins comprised of polyethylene,polyethylene copolymers, polypropylene copolymers, or blends thereof.Depending upon the desired properties of the film, the minority layersmay or may not have the same composition. The melt index of the resinsselected for the minority layers may range from 0.5 g/10 min. @ 190°C./2.16 kg to 12 g/10 min. @ 190° C./2.16 kg, with a preferred meltindex ranging from 3 g/10 min. @ 190° C./2.16 kg to 5 g/10 min. @ 190°C./2.16 kg. The density of the resins selected for the minority layersmay range from 0.850 g/cm³ to 0.969 g/cm³, with a preferred density ofapproximately 0.917 g/cm³.

To impart cling to the film, a cling agent may be incorporated into thefilm. The cling agent may be a migratory or non-migratory additive. Forexample, a migratory cling agent may be metered into a three-layer filmthrough one or both extruders for the minority layers. As anotherexample, if the film is composed of a single layer, a migratory clingagent may be metered into the film through the extruder for that layer.The rate at which the migratory cling agent is metered into the film mayrange from 0 to 25 percent of the total film structure on aweight-to-weight basis, with a preferred rate of approximately 0.6percent of the total film structure on a weight-by-weight basis. As analternative, a non-migratory cling agent may be added to the minoritylayers at a rate of 0 to 25 percent of the total film structure on aweight-to-weight basis, with a preferred rate of approximately 1 percentof the total film structure on a weight-to-weight basis.

As an example, a polybutene polymer with a Saybolt Universal Viscosityof 14,900 SUS at 99.degree. C. with a number average molecular weight of2,060 may be used as a cling agent. The molecular weight of this clingagent is higher than the molecular weight of a cling agent typicallyused in stretch films (which is polybutene with a Saybolt UniversalViscosity of 3,000 SUS at 99.degree. C. with a number average molecularweight of 1,290). Unlike the typical cling agent, the higher molecularweight polybutene polymer may not require time to migrate to the film'ssurface. As a result, the film's cling properties may develop almostimmediately. In addition, the higher molecular weight polybutene polymermay be minimally affected over time or winding tension. As a result, theoriented film may be produced in-process, which is more cost-effectiveand efficient than the standard practice of producing master rolls offilm, storing the master rolls for several days while the clingdevelops, and then converting the master rolls into pre-stretched film.

Referring generally to FIG. 1, the steps 100 for producing oriented castfilm in-process, according to an embodiment of the present disclosure,are illustrated. Specifically, the steps may comprise producing a filmfrom molten resins 110, gauging the film 120, longitudinally slittingthe film into multiple sections 130, folding the edges of the film 140,oscillating the film 150, and winding the film onto a film roll 160 in amanner that prevents stacking of the edge folds and entraps air betweenthe layers of film. All of the steps may be performed along a singleproduction line. The steps may be performed in a different order, andone or more steps may be eliminated without departing from the scope ofthe present disclosure.

As shown in FIG. 2, a means for producing a film from molten resins 200may comprise one or more extruders 210 connected by transfer pipes 220to a die 230. The number of extruders 210 used in the apparatus maydepend upon the desired composition of the film. For example, if thefilm is desired to have a three-layer composition, then three extruders210 may be used. As another example, if the film has only a singlelayer, then one extruder 210 may be used.

The extruders 210 may be connected to a source 240 of stock resins. Theextruders 210 may heat the stock resins to a molten condition anddeliver the molten resins through the transfer pipes 220 to the die 230.The film may be extruded through the die 230 onto a casting roll 250.The casting roll 250 may be a 30-inch diameter matt casting roll with aset temperature. As an example, the set temperature of the casting rollmay range from 75.degree. F. to 100.degree. F., with a preferred valueof approximately 90.degree. F. The film may move from the casting rollto a secondary chill roll 260. The secondary chill roll may be a 20-inchdiameter mirror finish secondary chill roll with a set temperature. Asan example, the set temperature of the secondary chill roll may rangefrom 65.degree. F. to 90.degree. F., with a preferred value ofapproximately 85.degree. F.

Oriented film may be produced by a plurality of suitable methods. Whilethe present disclosure specifically relates to chill roll castingtechniques, it is to be understood that the present disclosure is not tobe limited to that type of film production method. The disclosedcompositions, systems, methods, and devices can be successfully employedwith other film production methods, including, but not limited to, blownfilm techniques and tubular bath extrusion.

As shown in FIG. 3, dies 310 in the cast stretch film industry aregenerally positioned vertically. The placement of the die 310 may affectthe melt curtain 320, which is defined as the distance between the end330 of the die 310 through which the film is extruded and the surface340 of the casting roll 250. The placement of the die 310 may alsoaffect the intercept angle 360, which is the angle at which the extrudedfilm initially contacts the surface 340 of the casting roll 250. Forexample, the intercept angle 360 for a vertical die 310 may beapproximately 90.degree.

Possible die configurations in the present disclosure may include, butare not limited to, angled, vertical, and horizontal. As shown in FIG.4, the present disclosure may use an angled die 410. When compared to avertical die 310, an angled die 410 may reduce the length of the meltcurtain 320 and the intercept angle 360 to the casting roll 250. As aresult, the molten resins contact the casting roll 250 more quickly,giving the molecules in the resins less time to lose their orientationbefore they are quenched and frozen in place by the temperature of thecasting roll 250 and the secondary chill roll 260. As a result, anangled die 410 may produce thin layers of film with increased machinedirection orientation more efficiently than a vertical die 310. Due tothe increased machine direction orientation, films produced by thepresent disclosure do not require stretching in a separate step.

As shown in FIG. 1, the film may undergo additional processing stepsonce formed. These steps may include, but are not limited to, gaugingthe film, longitudinally slitting the film into multiple sections,folding the edges of the film, oscillating the film, and winding thefilm onto a film roll.

As discussed above, oriented film may be produced by a plurality ofsuitable methods, including cast or blown film processes. Films producedvia the cast film process may be made and processed in the mannerpreviously described. The blown film process may use low blow-up ratiosand narrow die gaps to achieve the required orientation. Blown filmproducts may be comprised of single or multiple layers. However,multiple layers may be necessary if high melt index resins are to beused to prevent or minimize melt fracture and interfacial instability.The use of high molecular weight cling agents may also be required toachieve a commercially viable product.

As can be seen, the present disclosure provides compositions, methods,systems, and devices for producing oriented film in-process for use inthe stretch film market. In particular, the present disclosure relatesto the use of particular resins and an angled die to increase the levelof orientation in the film as it is formed, thus eliminating the need tostretch the film in a separate step. The present disclosure also relatesto the use of a cling agent which eliminates the storage timetraditionally required to develop the film's cling properties.

From the foregoing, it will be understood by persons skilled in the artthat compositions, devices, systems, and methods for producing orientedfilm in-process for use in the stretch film market have been provided.While the description contains many specifics, these should not beconstrued as limitations on the scope of the present disclosure, butrather as an exemplification of the preferred embodiments thereof. Theforegoing is considered as illustrative only of the principles of thepresent disclosure. Further, because numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the present disclosure to the exact methodology shown anddescribed, and accordingly all suitable modifications and equivalentsmay be resorted to, falling within the scope of the present disclosure.Although this disclosure has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand numerous changes in the details of the method may be resorted towithout departing from the spirit and scope of the present disclosure.

1. An apparatus for producing oriented film in-process, said apparatuscomprising: a heated enclosure for heating a resin composition to apredetermined temperature that is equal to or greater than an associatedmelting temperature for said resin composition; a die disposed in fluidcommunication with said heated enclosure for extruding a curtain ofmelted resin; and a casting roll for receiving the curtain of meltedresin.
 2. The apparatus of claim 1, further comprising a secondary chillroll for receiving and quenching said curtain of melted resin.
 3. Theapparatus of claim 1, wherein said die is disposed at an approximatelyperpendicular angle measured relative to the plane of the curtain ofmelted resin as said curtain travels from the die to the casting roll.4. The apparatus of claim 1, wherein said die is disposed at anapproximately horizontal angle measured relative to the plane of thecurtain of melted resin as said curtain travels from the die to thecasting roll.
 5. The apparatus of claim 1, wherein said die is disposedat an angle between approximately perpendicular and approximatelyhorizontal measured relative to the plane of the curtain of melted resinas said curtain travels from the die to the casting roll.
 6. Theapparatus according to claim 5, wherein said die is disposed at an angleof less than about 90° measured relative to the plane of the curtain ofmelted resin as said curtain travels from the die to the casting roll.7. The apparatus of claim 1, wherein said curtain of melted resin ismeasured with respect to a distance established between the die and areceiving surface of said casting roll.
 8. The apparatus of claim 7,wherein said die is disposed at an angle between approximatelyperpendicular and approximately horizontal measured relative to theplane of the curtain of melted resin as said curtain travels from thedie to the casting roll, and a reduced distance between the die and areceiving surface of said casting roll is achieved.
 9. The apparatus ofclaim 8, wherein said die is disposed at an angle between approximatelyperpendicular and approximately horizontal measured relative to theplane of the curtain of melted resin as said curtain travels from thedie to the casting roll, and a plurality of resulting film layers havingan increased machine direction orientation is achieved.
 10. Theapparatus of claim 8, wherein said die is disposed at an angle of lessthan about 90° measured relative to the plane of the curtain of meltedresin as said curtain travels from the die to the casting roll.
 11. Amethod for producing oriented film in-process, said method comprising:heating a resin composition to a predetermined temperature that isgreater than an associated melting temperature for said resincomposition; transferring a quantity of melted resin to an associateddie; and extruding a curtain of melted resin from said die onto acasting roll.
 12. The method of claim 11, further comprisingtransferring said curtain of melted resin from said casting roll towarda secondary chill roll for quenching.
 13. The method of claim 11,further comprising disposing said die at an approximately perpendicularangle measured relative to the plane of the curtain of melted resin assaid curtain travels from the die onto the casting roll.
 14. The methodof claim 11, further comprising disposing said die at an approximatelyhorizontal angle measured relative to the plane of the curtain of meltedresin as said curtain travels from the die onto the casting roll. 15.The method of claim 11, further comprising disposing said die at anangle between approximately perpendicular and approximately horizontalmeasured relative to the plane of the curtain of melted resin as saidcurtain travels from the die onto the casting roll.
 16. The methodaccording to claim 15, further comprising disposing said die at an angleof less than about 90° measured relative to the plane of the curtain ofmelted resin as said curtain travels from the die onto the casting roll.17. The method of claim 11, further comprising measuring said curtain ofmelted resin with respect to a distance established between a diesurface from which the resin composition is extruded and a receivingsurface of said casting roll.
 18. The method of claim 17, furthercomprising disposing said die at an angle between approximatelyperpendicular and approximately horizontal measured relative to theplane of the curtain of melted resin as said curtain travels from thedie onto the casting roll, and establishing a reduced distance betweenthe die and a receiving surface of said casting roll.
 19. The method ofclaim 18, further comprising disposing said die at an angle betweenapproximately perpendicular and approximately horizontal measuredrelative to the plane of the curtain of melted resin as said curtaintravels from the die onto the casting roll, and extruding a plurality ofresulting film layers having an increased machine direction orientation.20. The method of claim 18, further comprising disposing said die at anangle of less than about 90° measured relative to the plane of thecurtain of melted resin as said curtain travels from the die onto thecasting roll.